I’ve actually had people complain that boards I make, are ‘‘too fast!’’ Both Kealoha, and Tiger, would frequently ask to borrow my Gun , on big days at Sunset. Thick fin and all. Not because the board was slow either. Draggy fins? That’s your term, and your flawed understanding. Understand one thing, if you can, I’m not selling or marketing anything. Trying to stimulate some out of the box thinking? Yes, I’m guilty of that. I find it comical that you had ‘‘sucky’’ experience with thick fins, at about the same time I was having excellent results with them. At those same Hawaiian breaks. Must have been the foil or shape on your fins. Whatever the reason, for our different experiences, It has colored our thinking about what works best.
“I find it comical that you had ‘‘sucky’’ experience with thick fins, at about the same time I was having excellent results with them. Must have been the foil or shape on your fins.”
Not necessarily a “must” there- you are very narrow-minded and too focussed on what results you want to see at the end.
It could be some other variable, of which there are many. The “Thick foil fins” at that time were from Brewer, who’s stated purpose was to try and push the same idea as yours, that thick foils are often more accurate and thus more efficient and “faster.” But some there on the North Shore made wonderfully accurate and efficient foils thinner which are faster in straight line situations than accurate thick ones. Go back and watch the great videos posted earlier showing actual science of flow and foil and drag. And “feel” is sometimes very different from reality, as many here have pointed out.
" Draggy fins? That’s your term, and your flawed understanding"
Thats my term, yours is:
“Increasing the drag on you fin…”
So its not really different nor a flawed understanding is it?
“Understand one thing, if you can, I’m not selling or marketing anything”
I was under the impression from another thread you were pushing a textured coating. Whether you have actually been successful in actually selling that story is another issue.
And here is what you said in that post ( sure sounds like marketing plans)
“In the future I hope to offer either fins for sale, or license the process to an existing fin maker, or perhaps provide a service to modify existing fins. Yet to be done is to combine the new foil configuration with a textured fin surface.”
By todays standards, those Reverse Fins of the early to mid 60’s were in fact too much fin. But lots of folks like to get a taste of what surfing was like in that era.
Did you make the hurricane swell this weekend? It was nice Saturday morning. I was out of the water by 11am. The current was starting to pick up and some of the guys from lighthouse were getting out down the beach where I normally surf. Otherwise some nice sets were coming in.
Had a busy weekend surfing, and attempting to make surfboards, and playing with family, but I guess this warrants a response.
As can be seen by the video, or real life if you surf, the surfer at no point is in uniform circular motion, which is when this formula would be applicable.
To see this note, the formula F=mV^2/r is normally derived when we assume a constant radial velocity, i.e., uniform circular motion. In non-uniform circular motion, there many other forces working on the surfer/surfboard, in particular there is the tangent vector to the waves surface, gravity, etc… In addition we have to account for drag on the water’s surface. I do not claim that we need do all of this to get some “back of the envelope” calculations, but using your formula which is associated with uniform circular motion is grossly inaccurate, and why I mentioned it would be a poor choice to continue to post it in every thread. It is definitely not accurate enough to affect fin choice.
A detailed explanation is here:
Although the internet is free so you are more then welcome to post whatever you would like.
To answer about an affordable accelerometer, …
First off since we are in non-uniform circular gravitational force is part of the centripetal accelaration, i.e. outward force. Think of like this, if we put a ball on a rope, if you spin it in the horizontal plane, for the most part this is uniform circular motion, if you spin it in the vertical plane this is nonuniform circular motion, because when it is falling gravity is “pushing it down” . Anyways this is neither here or there, the device I mentioned combines an accelerometer, magnetometer, and gyro. That along with a gps can provide pretty accurate measurements. In particular in detection and estimation, we use what is called a Kalman filter, that combines a bunch of noisy estimates into a pretty good estimate. This is what was used in guidance systems. So the gps can be pretty inaccurate, but by using the previously mentioned sensors you can get an accurate estimate of your path. In addition, depending on the location, you can use WAAS which gives a better position estimate. Basically as was mentioned you place the sensor by the leash plug, you know how long the board is, you can then calculate the accelaration felt on any part of the board.
The problem with a water wheel is that it will give you your speed relative to the water, which would be fine if the water wasn’t moving pretty fast up the face of the wave.Although it would be useful to give you speed estimates to see what the fin is exposed to.
On another note if you would like to know how to differentiate the effect of a rail and fin, once again** this goes back to my original point which was the equations you post are meaningless. The only thing that is going to work in this arena is to try fins put them on a surfboard and see how they surf. If you don’t trust what anyone has to say about the performance of fins and call you would like to call it mysticism, then you are going to have to put sensors on the board to take measurements. You will have to do a detailed experiment, in particular choose a board design you want to optimize and then try a bunch of different fins in it, i.e. the scientific method, pretty much what Thrailkill has done over the past 50ish years. My second point was that sure you can take readings from all these sensors, but the feeling is subjective.** I surfed a fugly green board I made this weekend in some fast bumpy surf, sensor wise it would like good, because it went fast, and I stayed on the wave for a while. Feeling wise it sucked. It was hard on my ankles and bumpy as hell, still a rush though:)
Next up, I had seen your post before about the unladen swallow, it was a rhetorical question. Although I am glad it resulted in the posting of an actual detailed scientific analysis of something. Although it had nothing to do with surfboards, or surfing in general. In your defense it did result in a picture of boobies, so that can’t be bad.
Hi Jason, we were on emergency management schedules at work. I had to work from 6am so I missed the morning. By the afternoon it was an ugly mess. Haven’t been in the water since I cut my foot.
I too have real experience with riding – not just surfboards. I am confident the centripetal acceleration/force equation gives a reasonably good estimate of G-Force based on my rides. No the turn is not a perfect circle, not likely a big difference for surfboard turns. Actually, I believe surfboard turns (etc.) are more of a spiral decay with radius decreasing to maintain sufficient centripetal force, preventing the rider from falling off the board and into the water.
Furthermore plus-one-shaper, George Gall, offered empirical data about G-Force in surfboard turns a while back. He measured G-Force on a hard pegged turn at close to 4-G. Making my quick mathematical estimates look close but still conservative…
Regarding your guidance system acclerometer, I doubt it is cheap.
Flow sensor, I am not talking about a wheel or propeller type flow-meter, something closer to a hotwire anemometer. But that specific device would not be particularly practical either. A radar sensor might work well for measuring water flow rates but, definitely not cheap.
I suspect the GPS used in the video had something more like +/- 5-10 meter horizontal accuracy and at best a +/- 15-20 meter accuracy for vertical position changes. Yep flow sensor measurements with and against upward water movement would be skewed. But I believe that data could be useful for fin-speed performance assessment, and potentially adjusted accordingly.
I am not interested continuing these fin debates, so I am typing quickly. My original point and that of an engineer, hans, was that drag does not increase speed. Maybe higher average speed over the entire ride.
Regardless, my principal points about centripetal accerlation/force have been and continue to be:
Making a simple turn or cutback does not increase speed. (IMO pumping is not turning.)
Cetripetal acceleration from turns results in increased “G-force.”
Fins and rails affect the G-Force attainable in a turn.
The G-force generated is more than enough to cause a surfboard to flex.
I believe the senations associated with turns (speed and drive) are the result of human sensory perception of increasing G-force – other neural responses as well.
We could digress about the human body’s inner ear and kinesthetic receptor responses to G-force and sensory perceptions of it. But that would likely generate another long, tedious discussion and debate. From there, we might further digress about the cause of speed wobble…
Yah, I don’t believe drag(increased friction?) increases speed either. But, I do know a nice homemade round pin with a well foiled thick fin on a fast hollow wave is pure joy… Plus, I know what causes speed wobble. Going too fast. Hah! Mike
Yep, all I was trying to say was that, look at a big bottom turn, the G’s from centripetal accelaration experienced at the bottom of the turn isn’t just the uniform circular motion, but gravity needs to be taken into account and you will get pretty close to the 4Gs. i.e., mv^2/r not going to cut it, period. As stated before if we fudge a little and look at an object moving in the horizontal plane in a circle mv^2/r is golden. If you do it in a vertical plane like almost all turns in surfing, you must take into account gravity. That is the last time I will attempt to explain
The sensor I posted was $80. A full system with GPS could probably be made for $200. I have been thinking about it, but would rather build a surfboard.
There was no gps in the video it was the sensor I mentioned with accelerometer, gyrometer, etc… It is pretty accurate with regard to measuring orientation, and acceleration.
Science should be shared to increase our knowledge, and help in our understanding of the world, ie. a positive thing.
Sorry to everyone else, I guess this is what happens when “keeping it real goes wrong”,
Keeping in mind the original surfboard speed premise, “pretty accurate” may not be good enough for determining vertical velocity in a range of 2-4 meters +/- instrument accuracy and precision (variability).
EDIT: The turns pictured below are pretty much horizontal. In many instances, bottom turns are mostly, if not soley horizontal – in the trough or flats. Not much vertical motion, up or down…
Camber is the shape of the line off which the upper and lower surface offsets are taken, a symmetrical foil will have flat or zero camber.
Why do some people feel the need to reinvent and misinterpret technology that has been around for close to 80 years. Foil geometry is well defined and documented, take a little time to study the books, or take advice, but this really doesn’t need reinventing.
Well, it does. But, it MUST be confined to the fin ONLY. And then on an almost nano scale. Something the brainiacs, in their zeal to nay-say, overlooked. Not having had the experience, they fail to grasp the concept. It has to do with sustaining attached flow, on the fin, over a wide range of AoA. And, most importantly, both the board and the fin must be reasonably well designed, and foiled. You’ve experienced a glimmer of that, with the fin that Dave made for you. Surprised you, by how much of a difference it made, eh?
Bill, drag acts opposite to forward motion, a net icrease in drag will lead to a slower board a net decrease in drag will lead to a faster board. Do you agree?
Bill, drag acts opposite to forward motion, a net icrease in drag will lead to a slower board a net decrease in drag will lead to a faster board. Do you agree?
